Synthesis Of Epoxy Sizing Agent And Its Effect On Interfacial Properties Of Carbon Fiber/epoxy Resin Composites

Because of its high specific modulus and high specific strength,carbon fiber reinforced polymer composites(CFRP)are replacing traditional metal materials and ceramic materials in various high-performance structural and functional applications,and are widely used in aerospace,industry,sporting goods,livelihood supplies,and other fields.The performance of CFRP is highly dependent on the fiber-resin interface,and good interface transfer properties can significantly improve the performance of composites.However,the surface of CFs is inert,and its wettability with resin and interfacial bonding force are not good,which dramatically affects the mechanical properties of CFRP.Coating sizing agent on the surface of CFs is an effective way to improve the interfacial properties.To improve the interfacial bonding abilities between CFs and epoxy resin,based on polyether glycidyl ester,three new epoxy self-emulsifying sizing agents were developed and prepared in this paper.At the same time,to improve the storage stabilities of the sizing agents,this study was based on maleic acid(anhydride),and the sulfonic acid group addition reaction was used to increase the hydrophilicity of the sizing agent molecule.The first sizing agent mainly studies the effect of the average molecular weight of polyethylene glycol(PEG)on the stabilities of the sizing agent emulsions and their performance.Firstly,the hydroxyl groups at both ends of polyethylene glycol and maleic anhydride were used to generate terminal carboxyl groups by the ring-opening reaction.Then polyether glycidyl ester with good fluidity and catalyst were added to synthesize a linear unsaturated polyester structure with epoxy groups on both sides.Next,adding aqueous sodium hydrogen sulfite solution to the sulfonation reaction of unsaturated double bonds,and finally neutralizing the product to neutrality by using aqueous ammonium hydrogen carbonate solution to obtain a sizing agent emulsion.The experiment used PEG with different average molecular weights to carry out comparative experiments to adjust the hydrophilicity of the sizing agent molecules.When the average molecular weight of PEG is 800,the prepared sizing agent has the most suitable hydrophilicity,and its emulsion is stable.The emulsion particle size is about 122.9 nm,and the polydispersity index(PDI)is about 0.073.In the second sizing agent research,the method of rapid preparation of sizing agent emulsion was explored,using maleic acid to react with polyether glycidyl ester directly and then carry out sulfonation reaction and neutralization reaction.The hydrophilicity of the sizing agent molecule is adjusted by adjusting the ratio of the reactants epoxy resin and maleic acid.The reaction process is about 1 h.The final sizing agent emulsion has excellent stability,and the particle size of the emulsion is about 142 nm,the PDI is about 0.078.In the third sizing agent,fluorine-containing monomers were mainly used to prepare sizing agent molecules with appropriate hydrophilicity and excellent film-forming properties to improve the strength of the fiber-resin interface.First,maleic anhydride and trifluoroethanol were used for ring-opening reaction to generate trifluoroethyl maleic acid,and then epoxy resin and catalyst were added to synthesize linear fluorinated unsaturated polyester with epoxy end groups,Sulfonation reaction and neutralization reaction were carried out to obtain sizing agent molecules.By adjusting the ratio of the reactant epoxy resin and trifluoroethyl maleic acid to adjust the hydrophilic and lipophilic value of the sizing agent molecule.The final sizing agent emulsion has excellent stability,the particle size of the emulsion is about 96.14 nm,and the PDI is about 0.04.The synthesized sizing agent emulsions were diluted to 1 wt%and then the CFs was sized.The surface morphologies,elemental changes,surface energy of the CFs before and after sizing treatment and monofilament tensile strength were tested and analyzed by SEM,video dynamic contact angle,XPS,and monofilament tensile test.The results showed that after sizing,the grooves left on the surface of the CFs due to the production process were effectively filled,the fiber surface had a uniform sizing film,the tensile strength of the monofilament was improved,the dispersion of the monofilament strength was reduced,the chemical activity of the fiber surface was increased,and the surface energy of the fiber was increased.Unidirectional composite laminates were subjected to ILSS test using a universal tensile testing machine.The results showed that in the first sizing agent system,the ILSS of carbon fiber/epoxy composites after sizing with sizing agent synthesized by polyethylene glycol 800 has the greatest improvement,which is 11.22%higher than that without sizing.The ILSS of the composite material after sizing prepared by the rapid synthesis method was increased by about 10.39%.The ILSS improvement of fluorine-containing sizing agent for composite materials reached 18.34%;by contrast,the composite material after sizing with commercial sizing agent Takemoto S64 only increased by 12.21%.